Classification: Introduced Species. In Florida in the United States, established breeding populations of Nile monitors have been known to exist in different parts of the state since at least 1990. Genetic studies have shown that these introduced animals are part of the subpopulation that originates from West Africa, and now often is recognized as its own species, the West African Nile monitor. The vast majority of the established breeding population is in Lee County, particularly in the Cape Coral and surrounding regions, including the nearby barrier islands (Sanibel, Captiva, and North Captiva), Pine Island, Fort Myers, and Punta Rassa. Established populations also exist in adjacent Charlotte County, especially on Gasparilla Island. Other areas in Florida with a sizeable number of Nile monitor sightings include Palm Beach County just southwest of West Palm Beach along State Road 80. In July 2008, a Nile monitor was spotted in Homestead, a small city southwest of Miami. Other sightings have been reported near Hollywood, Naranja, and as far south as Key Largo in the Florida Keys. The potential for the established population of Nile monitors in Lee, Charlotte, and other counties in Florida, to negatively impact indigenous crocodilians, such as American alligators (Alligator mississippiensis), and American crocodiles (Crocodylus acutus), is enormous, given that they normally raid crocodile nests, eat eggs, and prey on small crocodiles in Africa. Anecdotal evidence indicates a high rate of disappearance of domestic pets and feral cats in Cape Coral.

Description: The Nile monitor is Africa's longest lizard. They grow from about 3 feet 11 inches to 7 feet 3 inches in length, with the largest specimens attaining 8 feet. In an average-sized specimen, the snout to vent length will be around 1 foot 8 inches. In body mass, adults have been reported to vary widely, one study claiming only 1.8 to 3.7 lbs., others state weights ranging from 13 to 33 lbs. in big monitors. Variations may be due to age or environmental conditions. Exceptionally large specimens may scale as much as 44 lbs., but this species weighs somewhat less on average than the bulkier rock monitor. They have muscular bodies, strong legs, and powerful jaws. Their teeth are sharp and pointed in juvenile animals and become blunt and peg-like in adults. They also possess sharp claws used for climbing, digging, defense, or tearing at their prey. Like all monitors, they have forked tongues, with highly developed olfactory properties. The Nile monitor has quite striking, but variable, skin patterns, as they are greyish-brown above with greenish-yellow barring on the tail and large, greenish-yellow rosette-like spots on their backs with a blackish tiny spot in the middle. Their throats and undersides are an ochre-yellow to a creamy-yellow, often with faint barring. Their nostrils are placed high on their snouts, indicating these animals are very well adapted for an aquatic lifestyle. They are also excellent climbers and quick runners on land.

Habitat: The Nile Monitor is a highly adaptable habitat generalist, being found in forest, savanna, woodland, bushland, varied aquatic habitats from mangroves to lakes and rivers, and numerous human-modified habitats. It requires the presence of some open areas for basking, and is typically associated with water particularly in the juvenile stage. While largely terrestrial as an adult, the Nile Monitor can also be found climbing trees and rocks, and it is a strong and active swimmer. When inactive it can be found basking on waterside vegetation, in trees, or on logs or rocks. This species eats most animal prey it can overpower, including both vertebrate and invertebrate prey items as well as crocodile eggs. In Southern Africa, adults feed regularly on freshwater crabs, while juveniles feed on frogs and invertebrates. In the dry season particularly, up to 50% of the diet can consist of carrion. It is also a predator of freshwater turtle nests. Animals may aestivate during the dry season in part of the range. Animals reach sexual maturity at 3 to 4 years of age. The female lays between 5 and 60 eggs, with reproduction often timed to coincide with the end of the wet season.

Range: Nile monitors are native to Sub-Saharan Africa and along the Nile. They are not found in any of the desert regions of Africa (notably Sahara, Kalahari and much of the Horn of Africa), however, as they thrive around rivers.

Found in these States: FL

Diet: Nile monitors feed on a wide variety of prey items, including fish, frogs, toads (even poisonous ones of the genera Breviceps and Sclerophrys), small reptiles (such as turtles, snakes, lizards, and young crocodiles), birds, rodents, other small mammals (up to domestic cats and young antelopes [Raphicerus]), eggs (including those of crocodiles, agamids, other monitor lizards, and birds), invertebrates (such as beetles, termites, orthopterans, crabs, caterpillars, spiders, millipedes, earthworms, snails, and slugs), carrion, human wastes, and feces.

Reproduction: Nile monitors are a polygynandrous species and will mate promiscuously. Males may reportedly fight each other in violent "wrestling matches," presumably due to competition for mating opportunities. Varanus niloticus breeds once annually, with the season starting in June and ending in October range-wide. Mating and egg laying usually follows the rainy season, which varies regionally. This season correlates with the development of the gonads. The testicles of males are enlarged from June until September while the females are being sought. Regression of the gonads subsequently occurs until January and then the cycle recommences.

After spring rains (August through September), the female excavates a hole in the ground or in an active termite nest and lays 20 to 60 eggs. This may take 2 to 3 days to complete. If she lays her eggs in a termite nest, the termites will repair the hole in their nest, and the monitor eggs develop inside. Eggs may take up to 1 year to hatch. The small young weigh an average 26 g upon hatching. After hatching, the young may need to wait for rain to soften the hard nest, or reportedly the mother monitor may return at the right time and open the nest to free the hatchlings. Once they have emerged, however, the baby Nile monitors are on their own.

Status: Listed as Least Concern in view of its wide distribution, presumed large population, and because it is unlikely to be declining fast enough to qualify for listing in a more threatened category.

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